The most famous thing that Bingham and Eaton found was a very strange sex ratio in the bones at Machu Picchu. Based on Eaton's analysis, they found that about 80% of the people buried there were women. This, to Bingham, meant that Machu Picchu had been the last refuge of the last Inca king, who retreated there with a group of sacred virgins.

However, this finding proved to be incorrect. Later analysis showed that Eaton was not really all that familiar with the bones of people of the Andes. They tend to be smaller and more delicate than the white and black people whose bones he was familiar with. Therefore, he mistook small, delicate men for women.